Turbine nozzles are commonly cast as vane doublets, i.e., arcuate segments with two vanes or airfoils per segment, in order to lower the cost of the casting. The doublet configuration, however, leads to high stress/strain in certain areas of the doublet, which can manifest itself in the form of cracks. Once cracks grow to a critical size, the component part must be removed from service and repaired to prevent it from failing catastrophically in the turbine.
In more modern designs of gas turbine nozzles, a common approach is to use a singlet configuration, i.e., one airfoil per segment, rather than the doublet configuration. The use of a singlet configuration eliminates much of the stress/strain that drives cracking in the doublet configuration, but typically, singlets are considerably more expensive to produce.